1. Field of the Invention
The present invention relates to a recording apparatus for recording an image on a sheet, for example, such as a printer, a copying machine, a facsimile, a word processor, an electronic typewriter, a computer and the like, and a sheet conveying apparatus used with such a recording apparatus.
2. Related Background Art
Conventionally, as recording apparatuses of this kind, for example, a recording apparatus of ink jet type for injecting ink onto a sheet in response to image information has been proposed. In such a recording apparatus of ink jet type (referred to as "ink jet recording apparatus" hereinafter), a recording medium (sheet) situated at a downstream side of a recording head in a sheet conveying direction is pinched between a convey roller or a member having spur-shaped projections on its outer peripheral surface and made of metal or resin or a member having disks made of material having high water-repellent ability (such members are referred to generically as "sheet hold-down member" hereinafter), and the sheet is conveyed by rotating the convey roller or the sheet hold-down member.
With the arrangement as mentioned above, after the ink is discharged from the recording head onto the sheet, even when the sheet hold-down member passes through on the ink adhered to the sheet in a condition that the ink is not adequately absorbed or dried, since, in the spur-shaped sheet hold-down member, only small areas of the tip ends of the projections are contacted with the sheet. And, since, in the disk-shaped sheet hold-down member, only sharp peripheral edges of the disks are contacted with the sheet and the member has the excellent water-repellent ability, the ink is not transferred to other portions on the sheet, thereby preventing the sheet from being smudged.
Further, there has been proposed a technique in which the sheet is conveyed by the sheet hold-down member while contacting the sheet hold-down member with a ink absorbing member to remove the ink adhered to the sheet hold-down member, thereby achieving the above-mentioned effect. Further, in a technique disclosed in the Japanese Patent Application Laid-open No. 8-165043, grooves are formed in the convey roller and the sheet hold-down member abuts against the grooves to clean the sheet hold-down member, thereby achieving the above-mentioned effect.
However, since the above-mentioned conventional sheet hold-down members have spur-shaped sharp projections or disks having sharp peripheral edges, the convey roller must be formed from material having small hardness such as rubber to prevent damage or wear of the sheet hold-down member. Thus, an outer diameter of the convey roller is varied with change in temperature due to linear expansion to change the conveying amount of the convey roller, or frictional coefficient of the convey roller is varied with change in temperature, endurance and time lapse to reduce the conveying force of the convey roller. Particularly when the recording is effected with high resolving power by the ink jet recording apparatus, unevenness in conveying accuracy caused by the above-mentioned problems affects a bad influence upon the image accuracy.
Further, when the absorbing member is urged against the sheet hold-down member, the rotation load of the sheet hold-down member is increased. When the grooves are formed in the convey roller and the sheet hold-down member abuts against the grooves, although the rotation load of the sheet hold-down member is not so increased, the cleaning ability is worsened in comparison with the usage of the absorbing member, and, thus, the service life of the apparatus is reduced.